Here's the deal with the Samples from this set, they were inserted into Beckett Baseball magazines. During this era, Beckett would contract with the manufacturer for 100 cards, stamped in both silver and gold, for 200 different cards (quantity of each is unknown). Beckett has published their list of the 100 cards they included, and this isn't one of them.
Now whether Donruss/Leaf made other players that did not get sent to Beckett, I'm not sure. This is the first I've seen like this (as well as the others you reported). My best guess is to add any of these "extras" individually as they are reported/discovered.
Please reopen the IR, but please amend the report to only request the addition of this one card (not the entire base set) and please reference this thread. Thanks.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).